Wideband Voltage-Controlled Oscillator Circuitry

ABSTRACT

An electronic device may include a transceiver with mixer circuitry that up-converts or down-converts signals based on a voltage-controlled oscillator (VCO) signal. The transceiver circuitry may include first, second, third, and fourth VCOs. Each VCO may include a VCO core that receives a control voltage and an inductor coupled to the VCO core. Fixed linear capacitors may be coupled between the VCO cores. A switching network may be coupled between the VCOs. Control circuitry may place the VCO circuitry in one of four different operating modes and may switch between the operating modes to selectively control current direction in each of the inductors. The VCO circuitry may generate the VCO signal within a respective frequency range in each of the operating modes. The VCO circuitry may exhibit a relatively wide frequency range across all of the operating modes while introducing minimal phase noise to the system.

This application is a continuation of U.S. patent application Ser. No.17/131,168, filed Dec. 22, 2020, which is hereby incorporated byreference herein in its entirety.

FIELD

This disclosure relates generally to electronic devices and, moreparticularly, to electronic devices with wireless circuitry.

BACKGROUND

Electronic devices are often provided with wireless communicationscapabilities. An electronic device with wireless communicationscapabilities has wireless communications circuitry with one or moreantennas. Wireless transceiver circuitry in the wireless communicationscircuitry uses the antennas to transmit or receive radio-frequencysignals.

Wireless transceiver circuitry typically includes a mixer forupconverting or downconverting input signals based on a local oscillatorsignal. The local oscillator signal is often produced usingvoltage-controlled oscillator circuitry. It can be challenging to designsatisfactory voltage-controlled oscillator circuitry for an electronicdevice.

SUMMARY

An electronic device may include wireless circuitry. The wirelesscircuitry may include transceiver circuitry that conveys radio-frequencysignals over an antenna. The transceiver circuitry may include mixercircuitry. The mixer circuitry may up-convert or down-convert signalsfor the transceiver based on a voltage-controlled oscillator (VCO)output signal. The transceiver circuitry may include VCO circuitry thatgenerates the VCO output signal. The VCO circuitry may include first,second, third, and fourth VCOs. Each VCO may include a VCO core thatreceives a control voltage and an inductor coupled between first andsecond terminals of the VCO core. Fixed linear capacitors may be coupledbetween the VCO cores. A switching network may be coupled between thefirst, second, third, and fourth VCOs. The switching network mayinclude, for example, butterfly switches coupled between different pairsof the VCO cores in parallel with the capacitors.

The electronic device may include control circuitry. The controlcircuitry may provide control signals to the switching network to placethe VCO circuitry in one of four different operating modes. The controlcircuitry may switch between the operating modes to selectively controlcurrent direction in each of the inductors. The VCO circuitry maygenerate the VCO output signal within a respective frequency range ineach of the operating modes. The VCO circuitry may exhibit a relativelywide frequency range across all of the operating modes while introducingminimal phase noise to the system.

An aspect of the disclosure provides voltage-controlled oscillator (VCO)circuitry. The VCO circuitry can have a plurality of VCOs including afirst VCO having a first inductor, a second VCO having a secondinductor, a third VCO having a third inductor, and a fourth VCO having afourth inductor. The VCO circuitry can have a first pair of capacitorscoupled between the first VCO and the second VCO. The VCO circuitry canhave a second pair of capacitors coupled between the second VCO and thethird VCO. The VCO circuitry can have a third pair of capacitors coupledbetween the third VCO and the fourth VCO. The VCO circuitry can have afourth pair of capacitors coupled between the fourth VCO and the firstVCO. The VCO circuitry can have a switching network communicativelycoupled to the plurality of VCOs and configured to selectively controlcurrent direction in the first inductor, the second inductor, the thirdinductor, and the fourth inductor to generate VCO output signals infrequency ranges across at least four operating modes of the VCOcircuitry.

An aspect of the disclosure provides voltage-controlled oscillator (VCO)circuitry. The VCO circuitry can include a first VCO having a first VCOcore and a first inductor coupled to the first VCO core. The VCOcircuitry can include a second VCO having a second VCO core and a secondinductor coupled to the second VCO core. The VCO circuitry can include afirst pair of fixed capacitors coupled between the first VCO core andthe second VCO core. The VCO circuitry can include a first switchingcircuit coupled between the first VCO core and the second VC core inparallel with the first pair of fixed capacitors.

An aspect of the disclosure provides an electronic device. Theelectronic device can have baseband processor circuitry configured togenerate baseband signals. The electronic device can have mixercircuitry configured to generate radio-frequency signals based on thebaseband signals and a voltage-controlled oscillator (VCO) outputsignal. The electronic device can have an antenna configured to transmitthe radio-frequency signals. The electronic device can have VCOcircuitry configured to generate the VCO output signal. The VCOcircuitry can have a first VCO core with first and second terminals. TheVCO circuitry can have a first inductor coupled between the first andsecond terminals. The VCO circuitry can have a second VCO core withthird and fourth terminals. The VCO circuitry can have a second inductorcoupled between the third and fourth terminals. The VCO circuitry canhave a first fixed capacitor that couples the first terminal to thefourth terminal. The VCO circuitry can have a second fixed capacitorthat couples the second terminal to the third terminal. The VCOcircuitry can have a switching circuit that couples the first and secondterminals to the third and fourth terminals in parallel with the firstand second fixed capacitors, where the switching circuit has first andsecond states, in the first state the switching circuit couples thefirst terminal to the fourth terminal and couples the second terminal tothe third terminal, and in the second state the switching circuitcouples the first terminal to the third terminal and couples the secondterminal to the fourth terminal in the second state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an illustrative electronicdevice having a transceiver with voltage-controlled oscillator (VCO)circuitry in accordance with some embodiments.

FIG. 2 is a diagram of illustrative VCO circuitry having multiple VCOsthat are coupled together using fixed capacitors and a switching networkfor extending a frequency range of the VCO circuitry in accordance withsome embodiments.

FIG. 3 is a circuit diagram of an illustrative VCO core in accordancewith some embodiments.

FIG. 4 is a circuit diagram of an illustrative butterfly switch that maybe formed in a switching network coupled between VCOs in accordance withsome embodiments.

FIG. 5 is a flow chart of illustrative operations that may be performedin generating VCO output signals using VCO circuitry in accordance withsome embodiments.

FIGS. 6-9 are diagrams showing how illustrative VCO circuitry may beused to generate VCO signals in respective first, second, third, andfourth operating modes in accordance with some embodiments.

FIG. 10 is a plot showing how operating illustrative VCO circuitry inthe first, second, third, and fourth operating modes of FIGS. 6-9 mayserve to maximize the frequency range of the VCO circuitry in accordancewith some embodiments.

DETAILED DESCRIPTION

Electronic device 10 of FIG. 1 may be a computing device such as alaptop computer, a desktop computer, a computer monitor containing anembedded computer, a tablet computer, a cellular telephone, a mediaplayer, or other handheld or portable electronic device, a smallerdevice such as a wristwatch device, a pendant device, a headphone orearpiece device, a device embedded in eyeglasses or other equipment wornon a user's head, or other wearable or miniature device, a television, acomputer display that does not contain an embedded computer, a gamingdevice, a navigation device, an embedded system such as a system inwhich electronic equipment with a display is mounted in a kiosk orautomobile, a wireless internet-connected voice-controlled speaker, ahome entertainment device, a remote control device, a gaming controller,a peripheral user input device, a wireless base station or access point,equipment that implements the functionality of two or more of thesedevices, or other electronic equipment.

As shown in the functional block diagram of FIG. 1, device 10 mayinclude components located on or within an electronic device housingsuch as housing 12. Housing 12, which may sometimes be referred to as acase, may be formed of plastic, glass, ceramics, fiber composites, metal(e.g., stainless steel, aluminum, metal alloys, etc.), other suitablematerials, or a combination of these materials. In some situations,parts or all of housing 12 may be formed from dielectric or otherlow-conductivity material (e.g., glass, ceramic, plastic, sapphire,etc.). In other situations, housing 12 or at least some of thestructures that make up housing 12 may be formed from metal elements.

Device 10 may include control circuitry 14. Control circuitry 14 mayinclude storage such as storage circuitry 16. Storage circuitry 16 mayinclude hard disk drive storage, nonvolatile memory (e.g., flash memoryor other electrically-programmable-read-only memory configured to form asolid-state drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Storage circuitry 16 may include storagethat is integrated within device 10 and/or removable storage media.

Control circuitry 14 may include processing circuitry such as processingcircuitry 18. Processing circuitry 18 may be used to control theoperation of device 10. Processing circuitry 18 may include on one ormore microprocessors, microcontrollers, digital signal processors, hostprocessors, baseband processor integrated circuits, application specificintegrated circuits, central processing units (CPUs), etc. Controlcircuitry 14 may be configured to perform operations in device 10 usinghardware (e.g., dedicated hardware or circuitry), firmware, and/orsoftware. Software code for performing operations in device 10 may bestored on storage circuitry 16 (e.g., storage circuitry 16 may includenon-transitory (tangible) computer readable storage media that storesthe software code). The software code may sometimes be referred to asprogram instructions, software, data, instructions, or code. Softwarecode stored on storage circuitry 16 may be executed by processingcircuitry 18.

Control circuitry 14 may be used to run software on device 10 such assatellite navigation applications, internet browsing applications,voice-over-internet-protocol (VOIP) telephone call applications, emailapplications, media playback applications, operating system functions,etc. To support interactions with external equipment, control circuitry14 may be used in implementing communications protocols. Communicationsprotocols that may be implemented using control circuitry 14 includeinternet protocols, wireless local area network (WLAN) protocols (e.g.,IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols forother short-range wireless communications links such as the Bluetooth®protocol or other wireless personal area network (WPAN) protocols, IEEE802.11ad protocols (e.g., ultra-wideband protocols), cellular telephoneprotocols (e.g., 3G protocols, 4G (LTE) protocols, 5G protocols, etc.),antenna diversity protocols, satellite navigation system protocols(e.g., global positioning system (GPS) protocols, global navigationsatellite system (GLONASS) protocols, etc.), antenna-based spatialranging protocols (e.g., radio detection and ranging (RADAR) protocolsor other desired range detection protocols for signals conveyed atmillimeter and centimeter wave frequencies), or any other desiredcommunications protocols. Each communications protocol may be associatedwith a corresponding radio access technology (RAT) that specifies thephysical connection methodology used in implementing the protocol.

Device 10 may include input-output circuitry 20. Input-output circuitry20 may include input-output devices 22. Input-output devices 22 may beused to allow data to be supplied to device 10 and to allow data to beprovided from device 10 to external devices. Input-output devices 22 mayinclude user interface devices, data port devices, and otherinput-output components. For example, input-output devices 22 mayinclude touch sensors, displays (e.g., touch-sensitive and/orforce-sensitive displays), light-emitting components such as displayswithout touch sensor capabilities, buttons (mechanical, capacitive,optical, etc.), scrolling wheels, touch pads, key pads, keyboards,microphones, cameras, buttons, speakers, status indicators, audio jacksand other audio port components, digital data port devices, motionsensors (accelerometers, gyroscopes, and/or compasses that detectmotion), capacitance sensors, proximity sensors, magnetic sensors, forcesensors (e.g., force sensors coupled to a display to detect pressureapplied to the display), etc. In some configurations, keyboards,headphones, displays, pointing devices such as trackpads, mice, andjoysticks, and other input-output devices may be coupled to device 10using wired or wireless connections (e.g., some of input-output devices22 may be peripherals that are coupled to a main processing unit orother portion of device 10 via a wired or wireless link).

Input-output circuitry 20 may include wireless circuitry 24 to supportwireless communications. Wireless circuitry 24 (sometimes referred toherein as wireless communications circuitry 24) may include one or moreantennas 40. Wireless circuitry 24 may also include baseband processorcircuitry, transceiver circuitry, amplifier circuitry, filter circuitry,switching circuitry, radio-frequency transmission lines, and/or anyother circuitry for transmitting and/or receiving radio-frequencysignals using antenna(s) 40.

For example, as shown in FIG. 1, wireless circuitry 24 may includeradio-frequency transceiver circuitry such as transceiver circuitry 28that transmits and/or receives radio-frequency signals within acorresponding frequency band at radio frequencies (sometimes referred toherein as a communications band or simply as a “band”). For example,transceiver circuitry 28 may handle wireless local area network (WLAN)frequency bands (e.g., Wi-Fi® (IEEE 802.11) or other WLAN communicationsbands) such as a 2.4 GHz WLAN band (e.g., from 2400 to 2480 MHz), a 5GHz WLAN band (e.g., from 5180 to 5825 MHz), a Wi-Fi® 6E band (e.g.,from 5925-7125 MHz), and/or other Wi-Fi® bands (e.g., from 1875-5160MHz), wireless personal area network (WPAN) frequency bands such as the2.4 GHz Bluetooth® band or other WPAN communications bands, cellulartelephone frequency bands (e.g., bands from about 600 MHz to about 5GHz, 3G bands, 4G LTE bands, 5G New Radio Frequency Range 1 (FR1) bandsbelow 10 GHz, 5G New Radio Frequency Range 2 (FR2) bands between 20 and60 GHz, etc.), other centimeter or millimeter wave frequency bandsbetween 10-300 GHz, near-field communications frequency bands (e.g., at13.56 MHz), satellite navigation frequency bands (e.g., a GPS band from1565 to 1610 MHz, a Global Navigation Satellite System (GLONASS) band, aBeiDou Navigation Satellite System (BDS) band, etc.), ultra-wideband(UWB) frequency bands that operate under the IEEE 802.15.4 protocoland/or other ultra-wideband communications protocols, communicationsbands under the family of 3GPP wireless communications standards,communications bands under the IEEE 802.XX family of standards, and/orany other desired frequency bands of interest. Transceiver circuitry 28may sometimes be referred to herein as transceiver 28.

Transceiver circuitry 28 may be coupled to one or more antennas 40 overone or more radio-frequency transmission lines such as radio-frequencytransmission line 36. Transmission lines in device 10 such asradio-frequency transmission line 36 may include coaxial cables,microstrip transmission lines, stripline transmission lines,edge-coupled microstrip transmission lines, edge-coupled striplinetransmission lines, transmission lines formed from combinations oftransmission lines of these types, etc. Antennas 40 may be formed usingany desired antenna structures. For example, antennas 40 may includeantennas with resonating elements that are formed from loop antennastructures, patch antenna structures, inverted-F antenna structures,slot antenna structures, planar inverted-F antenna structures, helicalantenna structures, monopole antennas, dipoles, hybrids of thesedesigns, etc. Filter circuitry, switching circuitry, impedance matchingcircuitry, and/or other antenna tuning components may be adjusted toadjust the frequency response and wireless performance of antennas 40over time.

Wireless circuitry 24 may also include baseband processor circuitry suchas baseband processor 26. Baseband processor 26 may be coupled totransceiver circuitry 28 over baseband path 30. While control circuitry14 is shown separately from wireless circuitry 24 in the example of FIG.1 for the sake of clarity, wireless circuitry 24 may include processingcircuitry that forms a part of processing circuitry 18 and/or storagecircuitry that forms a part of storage circuitry 16 of control circuitry14 (e.g., portions of control circuitry 14 may be implemented onwireless circuitry 24, baseband processor 26, etc.).

The example of FIG. 1 is merely illustrative. In general, wirelesscircuitry 24 may include any desired number of baseband processors 26,any desired number of transceivers, and any desired number of antennas40. Each baseband processor 26 may be coupled to one or moretransceivers over respective baseband paths 30. Each transceiver mayinclude transmitter circuitry that outputs uplink signals to antenna(s)40 and/or may include receiver circuitry that receives downlink signalsfrom antenna(s) 40. Each transceiver may be coupled to one or moreantennas 40 over respective radio-frequency transmission lines 36. Oneor more of the radio-frequency transmission lines may have aradio-frequency front end module interposed thereon. The radio-frequencyfront end module may include radio-frequency front end components suchas filters, switches, impedance matching circuitry, antenna tuningcomponents, amplifier circuitry, radio-frequency couplers, sensors,etc., mounted to a common package, chip, or substrate.

In performing wireless transmission, baseband processor 26 may providebaseband signals BB to transceiver circuitry 28 over baseband path 30.Transceiver circuitry 28 may include circuitry for converting thebaseband signals BB received from baseband processor 26 intocorresponding radio-frequency signals. For example, transceivercircuitry 28 may include mixer circuitry such as one or more mixers 34for up-converting (or modulating) baseband signals BB to radiofrequencies prior to transmission over antenna(s) 40 (e.g., asradio-frequency signals SIGRF). Transceiver circuitry 28 may alsoinclude digital-to-analog converter (DAC) and/or analog-to-digitalconverter (ADC) circuitry for converting signals between digital andanalog domains (not shown in FIG. 1 for the sake of clarity). Antenna(s)40 may transmit radio-frequency signals SIGRF to external wirelessequipment by radiating the radio-frequency signals into free space.

In performing wireless reception, antenna(s) 40 may receiveradio-frequency signals SIGRF from the external wireless equipment. Thereceived radio-frequency signals SIGRF may be conveyed to transceivercircuitry 28 via radio-frequency transmission line 36. Transceivercircuitry 28 may include circuitry for converting the receivedradio-frequency signals into corresponding baseband signals. Forexample, transceiver circuitry 28 may use one or more mixers 34 todown-convert (or demodulate) the received radio-frequency signals SIGRFto baseband frequencies prior to conveying the received signals tobaseband processor 26 over baseband path 30 (e.g., as baseband signalsBB).

In order to perform up-conversion, mixer(s) 34 may mix a localoscillator (LO) signal such as local oscillator signal LO received overpath 38 with an input signal such as baseband signals BB. If desired,local oscillator signal LO may include multiple local oscillator signalsthat are provided to different mixers 34 for up-converting to differentfrequencies. For example, local oscillator signal LO may include aradio-frequency local oscillator (RFLO) signal for upconverting signalsfrom baseband to radio frequencies or for upconverting signals fromintermediate frequencies (IF) to radio frequencies (e.g., asradio-frequency signals SIGRF). In examples where intermediatefrequencies are used, local oscillator signal LO may also include anintermediate frequency local oscillator (IFLO) signal for upconvertingsignals from baseband to the intermediate frequencies. In examples wherethe radio frequencies are greater than 10 GHz (e.g., more than 20 GHz,more than 30 GHz, etc.), the intermediate frequencies may be betweenabout 100 MHz and 10 GHz, as an example. Use of intermediate frequenciesin scenarios where the radio frequencies are greater than 10 GHz mayallow the signals to be conveyed across relatively large distanceswithin device 10 with minimal signal attenuation, as high frequenciessuch as frequencies over 10 GHz are particularly susceptible toattenuation. Similarly, in order to perform down-conversion, mixer(s) 34may mix local oscillator signal LO with an input signal such asradio-frequency signals SIGRF to generate intermediate frequency signalsor baseband signals BB.

Transceiver circuitry 28 may include local oscillator circuitry such aslocal oscillator 32 that produces local oscillator signals LO. In animplementation that is described herein as an example, local oscillator32 may include voltage-controlled oscillator circuitry such asvoltage-controlled oscillator (VCO) circuitry 42. VCO circuitry 42 mayoutput periodic signals on path 38, sometimes referred to herein as VCOoutput signals OSC, based on a control voltage such as control voltageV_(CTRL), received over control path 44 (e.g., from control circuitry14). Local oscillator 32 may generate local oscillator signals LO basedon VCO output signals OSC. For example, local oscillator 32 may includea phase-locked loop (PLL), digital flip-flops, buffer circuits, and/orany other desired circuitry (e.g., clocking circuitry) that produceslocal oscillator signals LO using the VCO output signals OSC generatedby VCO circuitry 42. The example of FIG. 1 is merely illustrative. VCOcircuitry 42 need not be formed as a part of local oscillator 32. Ingeneral, VCO output signals OSC may be used to perform any desiredfunctions for device 10 that otherwise require VCO output signals suchas VCO output signals OSC.

Control voltage V_(CTRL), may be used to control the frequency of VCOoutput signals OSC and thus the frequency of local oscillator signals LO(e.g., for controlling mixer(s) 34 to down-convert or up-convert inputsignals to desired frequencies). In an implementation that is describedherein as an example, VCO circuitry 42 includes multiplevoltage-controlled oscillators (VCOs). Forming VCO circuitry 42 withmultiple VCOs may serve to extend the total frequency range producibleby mixer(s) 34 relative to scenarios where the VCO circuitry includesonly a single VCO.

In some scenarios, switched capacitors (e.g., series-coupled switchesand capacitors) are coupled between different pairs of the VCOs.However, in practice, the ratio C_(ON)/C_(OFF) of the switchedcapacitors serves as a bottleneck for the frequency range producible byVCO circuitry 42. In addition, the switched capacitors may exhibit arelatively low Q-factor and can introduce undesirable phase noise intothe system. In order to further extend the frequency range producible byVCO circuitry 42 while mitigating these issues, VCO circuitry 42 may beformed without switched capacitors between the VCOs. Instead, VCOcircuitry 42 may include fixed linear capacitors and a separate,parallel-coupled, switching network coupled between the VCOs. Controlcircuitry 14 may provide switch control signals SW_(CTRL) over controlpath 44 to control the state of the switching network. The state of theswitching network may be controlled to place VCO circuitry 42 into oneof multiple different operating modes. In an example where VCO circuitry42 includes four VCOs, the switching network may be controlled to placeVCO circuitry 42 into one of four different operating modes. Eachoperating mode may be associated with a different respective frequencyrange producible using VCO circuitry 42. Forming VCO circuitry 42 inthis way may serve to maximize the frequency range producible using VCOcircuitry 42. In addition, the fixed linear capacitors may exhibitgreater linearity and greater Q-factor, thereby introducing less phasenoise, than in scenarios where switched capacitors are coupled betweenthe VCOs.

FIG. 2 is a diagram of VCO circuitry 42 in an example where VCOcircuitry 42 includes four VCOs for producing VCO output signals OSC.This example is merely illustrative and, in general, VCO circuitry 42may include two VCOs, six VCOs, more than six VCOs, or any other desirednumber of VCOs.

As shown in FIG. 2, VCO circuitry 42 may include four VCOs 50 such as afirst VCO 50A, a second VCO 50B, a third VCO 50C, and a fourth VCO 50D.Each VCO 50 may be formed on a common substrate such as a flexible orrigid printed circuit board substrate. Each VCO 50 may include acorresponding VCO core 54 having a first terminal N and a secondterminal P. VCO circuitry 42 may have tap points (output terminals) ateach of the terminals N and P of VCO cores 54A, 54B, 54C, and 54D (e.g.,for outputting VCO output signals OSC of FIG. 1). Each VCO core 54 mayreceive control voltage V_(CTRL) for tuning the frequency of VCO outputsignals OSC. Terminals N and P may be, for example, respective negativeand positive signal terminals of the VCO cores. In this example, VCOoutput signals OSC may be differential signals formed from adifferential signal pair output that is output from VCO circuitry 42 atterminals N and P (e.g., where the differential signal pair includes anegative signal output at terminal N and a corresponding positive signaloutput at terminal P).

Each VCO 50 may also include a respective inductor 52 that is coupledbetween terminals N and P of the corresponding VCO core 54. Eachinductor 52 can have one or more loops or coils of conductive materialsuch as conductive traces on the underlying substrate. For example, VCO50A may have an inductor 52A coupled between terminals N and P of VCOcore 54A, VCO 50B may have an inductor 52B coupled between terminals Nand P of VCO core 54B, VCO 50C may have inductor 52C coupled betweenterminals N and P of VCO core 54C, etc. Current may run around inductors52 while VCO circuitry 42 generates VCO output signals OSC.

The VCO circuitry 42 can have capacitors 56 coupled between pairs of theVCOs 50. The capacitors 56 can be fixed linear capacitors. In someembodiments, the capacitors 56 can be variable capacitors. Thecapacitors 56 may be coupled in parallel between adjacent pairs of theVCOs 50 in VCO circuitry 42. For example, as shown in FIG. 2, a firstpair of capacitors 56-1 may be coupled in parallel between VCOs 50A and50B. Capacitors 56-1 may include a first capacitor coupled betweenterminal P on VCO core 54A and terminal P on VCO core 54B and mayinclude a second capacitor coupled between terminal N on VCO core 54Aand terminal N on VCO core 54B. In addition, a second pair of capacitors56-2 may be coupled in parallel between VCOs 50B and 50C. Capacitors56-2 may include a first capacitor coupled between terminal P on VCOcore 54B and terminal P on VCO core 54C and may include a secondcapacitor coupled between terminal N on VCO core 54B and terminal N onVCO core 54C. Similarly, a third pair of capacitors 56-3 may be coupledin parallel between VCOs 50C and 50D. Capacitors 56-3 may include afirst capacitor coupled between terminal P on VCO core 54C and terminalP on VCO core 54D and may include a second capacitor coupled betweenterminal N on VCO core 54C and terminal N on VCO core 54D. Finally, afourth pair of capacitors 56-4 may be coupled in parallel between VCOs50D and 50A. Capacitors 56-4 may include a first capacitor coupledbetween terminal P on VCO core 54D and terminal P on VCO core 54A andmay include a second capacitor coupled between terminal N on VCO core54D and terminal N on VCO core 54A. While each of the capacitors 56 inFIG. 2 are shown as a single capacitor, each of the capacitors 56 shownin FIG. 2 may include multiple fixed linear capacitors, if desired.Capacitors 56 may be formed as metal-oxide-metal (MOM) capacitors on theunderlying substrate used to form VCO circuitry 42, if desired.

VCO circuitry 42 may also include switching circuitry such as switchnetwork 58 coupled between each of the VCOs 50 in VCO circuitry 42.Switch network 58 may be coupled to terminals N and P of each of the VCOcores 54 in VCO circuitry 42. In an implementation that is describedherein as an example, switch network 58 may include four switchingcircuits 70 (e.g., butterfly switches), where each switching circuit 70is coupled between a respective pair of the VCOs 50 in VCO circuitry 42in parallel with capacitors 56. For example, switch network 58 mayinclude a switching circuit 70 (e.g., butterfly switch) coupled betweenterminals P and N on VCO cores 54A and 54B (e.g., in parallel withcapacitors 56-1), a second switching circuit 70 coupled betweenterminals P and N on VCO cores 54B and 54C (e.g., in parallel withcapacitors 56-2), a third switching circuit 70 coupled between terminalsP and N on VCO cores 54C and 54D (e.g., in parallel with capacitors56-3), and a fourth switching circuit 70 coupled between terminals P andN on VCO cores 54D and 54A (e.g., in parallel with capacitors 56-4).

Control circuitry 14 (FIG. 1) may provide switch control signalSW_(CTRL) (FIG. 1) to switch network 58 to control the state of theswitching circuits 70 (e.g., the butterfly switches) in switch network58. The switching circuits 70 in switch network 58 may be adjusted toswitch VCO circuitry 42 between different operating modes. In theexample of FIG. 2, VCO circuitry 42 may have four different operatingmodes. This is merely illustrative and, in general, VCO circuitry 42 mayhave any desired number of operating modes. Each operating mode may beassociated with a different respective frequency range for VCO outputsignals OSC and thus a different respective frequency range producibleat mixer(s) 34 (e.g., using the local oscillator signals LO generatedusing VCO output signals OSC). Control circuitry 14 may place VCOcircuitry 42 in a selected one of the four operating modes at a giventime by controlling switch network 58 using switch control signalSW_(CTRL). Control circuitry 14 may further tune the frequency producedby VCO circuitry 42 using the control voltage V_(CTRL) provided to VCOcores 54. Interconnecting the VCOs 50 in VCO circuitry 42 using fixedlinear capacitors such as capacitors 56 and a parallel-coupled switchnetwork such as switch network 58 may serve to maximize the frequencyrange producible using VCO circuitry 54, while also minimizing phasenoise due to the high Q-factor and linearity of capacitors 56.

FIG. 3 is a circuit diagram of a given VCO core 54 in one exemplaryimplementation. VCO core 54 of FIG. 3 may be used to form one, more thanone, or each of the VCO cores 54A, 54B, 54C, and 54D in VCO circuitry42. As shown in FIG. 3, VCO core 54 may have a first set ofcross-coupled transistors M₁ and M₂ and a second set of cross-coupledtransistors M₃ and M₄ coupled between terminals P and N. VCO core 54 mayalso have one or more varactors such as varactor 60 coupled betweenterminals P and N in parallel with the cross-coupled transistors. Inaddition, one or more switched capacitors 62 may be coupled in parallelbetween terminals P and N (e.g., in parallel with the cross-coupledtransistors and varactor 60). Each switched capacitor 62 may include oneor more capacitors coupled in series with a switch.

Control voltage V_(CTRL) (FIGS. 1 and 2) may include control voltagesV_(a) and V_(b) provided to varactor 60, as well as control signals forcontrolling the switches in switched capacitors 62. The VCO outputsignals OSC produced by the corresponding VCO 50 may be output at tappoints coupled to terminals P and N (e.g., as a differential signalpair). Control circuitry 14 may control (fine-tune) the frequency of theVCO output signals OSC produced on terminals P and N using controlvoltages V_(a) and V_(b) as well as using the control signals thatcontrol the switches in switched capacitors 62. The example of FIG. 3 ismerely illustrative and, in general, VCO core 54 may be implementedusing any desired VCO core architecture.

FIG. 4 is a circuit diagram of a given switching circuit 70 in switchnetwork 58 of FIG. 2. Switching circuit 70 may be, for example, abutterfly switch. Switching circuit 70 may therefore sometimes bereferred to herein as butterfly switch 70. Switching circuit 70 may beused to couple terminals P and N of VCO core 54A to terminals P and N ofVCO core 54B, to couple terminals P and N of VCO core 54B to terminals Pand N of VCO core 54C, to couple terminals P and N of VCO core 54C toterminals P and N of VCO core 54D, or to couple terminals P and N of VCOcore 54D to terminals P and N of VCO core 54A. In other words, switchnetwork 58 may include four switching circuits 70 of FIG. 4, eachcoupled between a respective pair of adjacent VCO cores 54.

As shown in FIG. 4, switching circuit 70 may be coupled betweenterminals P1, P2, N1, and N2 in parallel with a pair of capacitors 56(e.g., capacitors 56-1, 56-2, 56-3, or 56-4 of FIG. 2). For example, inscenarios where switching circuit 70 is used to couple terminals P and Nof VCO core 54A to terminals P and N of VCO core 54B (e.g., in parallelwith capacitors 56-1 of FIG. 2), terminal P1 forms terminal P of VCOcore 54A, terminal P2 forms terminal P of VCO core 54B, terminal N1forms terminal N of VCO core 54A, and terminal N2 forms terminal N ofVCO core 54B. Similarly, in scenarios where switching circuit 70 is usedto couple terminals P and N of VCO core 54B to terminals P and N of VCOcore 54C (e.g., in parallel with capacitors 56-2 of FIG. 2), terminal P1forms terminal P of VCO core 54B, terminal P2 forms terminal P of VCOcore 54C, terminal N1 forms terminal N of VCO core 54B, and terminal N2forms terminal N of VCO core 54C. In addition, in scenarios whereswitching circuit 70 is used to couple terminals P and N of VCO core 54Cto terminals P and N of VCO core 54D (e.g., in parallel with capacitors56-3 of FIG. 2), terminal P1 forms terminal P of VCO core 54C, terminalP2 forms terminal P of VCO core 54D, terminal N1 forms terminal N of VCOcore 54C, and terminal N2 forms terminal N of VCO core 54D. Finally, inscenarios where switching circuit 70 is used to couple terminals P and Nof VCO core 54D to terminals P and N of VCO core 54A (e.g., in parallelwith capacitors 56-4 of FIG. 2), terminal P1 forms terminal P of VCOcore 54D, terminal P2 forms terminal P of VCO core 54A, terminal N1forms terminal N of VCO core 54D, and terminal N2 forms terminal N ofVCO core 54A.

Switching circuit 70 may include a first switch 72 that couples terminalP1 to terminal P2 and a second switch 72 that couples terminal N1 toterminal N2 (e.g., in parallel with the first switch 72 and capacitors56). Switching circuit 70 may also include crossed switches such as afirst switch 74 that couples terminal P1 to terminal N2 and a secondswitch 74 that couples terminal N1 to terminal P2. Each switch 72 andeach switch 74 may be a single-pole single-throw (SPST) switch, as oneexample. This is merely illustrative. In general, switches 72 and 74 maybe formed using any type of switch architecture. Switching circuit 70may include any desired number of switches arranged in other mannersbetween terminals P1, P2, N1, and N2 if desired.

Switch control signal SW_(CTRL), (FIG. 2) may control the states ofswitches 72 and 74. In an implementation that is described herein as anexample, switching circuit 70 may have first and second states(sometimes referred to herein as first and second switching states). Inthe first state, switches 72 are closed and switches 74 are open,thereby coupling terminal P1 to terminal P2 and coupling terminal N1 toterminal N2 (e.g., while de-coupling terminal P1 from terminal N2 andde-coupling terminal N1 from terminal P2). In the second state, switches74 are closed and switches 72 are open, thereby coupling terminal P1 toterminal N2 and coupling terminal N1 to terminal P2 (e.g., whilede-coupling terminal P1 from terminal P2 and de-coupling terminal N1from terminal N2).

When open, each switch 72 or 74 may form a very high impedance or verylow transconductance g_(m) through the switch (e.g., an impedance thatexceeds a threshold impedance value or a transconductance that is lessthan a threshold transconductance value). When closed, each switch 72 or74 may form a very low impedance or very high transconductance g_(m)through the switch (e.g., an impedance that exceeds a thresholdimpedance value or a transconductance that is less than a thresholdtransconductance value). As an example, switches such as switches 72 and74 may each be formed using transistors having source, drain, and gateterminals. Each switch may be closed or “turned on” by asserting a gatevoltage provided to the gate terminal to provide an electricalconnection between its source and drain terminals. Similarly, eachswitch may be opened or “turned off” by deasserting the gate voltage toprovide electrical isolation between its source and drain terminals.Switching circuit 70 may selectively couple ports P1 and N1 to ports P2and N2 without introducing loss or nonlinearity to the system. Switchingcircuit 70 may sometimes be referred to herein as phase swapper 70.

Each switching circuit 70 in switch network 58 (FIG. 2) may be placed ina selected one of the first and second states to place VCO circuitry 42in a selected one of the first, second, third, or fourth operatingmodes. Control circuitry 14 may place VCO circuitry 42 in a selected oneof the first, second, third, or fourth operating modes based on thefrequency to be produced by mixer(s) 34. FIG. 5 is a flow chart ofillustrative operations that may be performed by control circuitry 14and VCO circuitry 42 to produce VCO output signals OSC of FIG. 1.

At operation 76, control circuitry 14 may identify a frequency for VCOoutput signal OSC. The frequency of VCO output signal OSC may, forexample, be the VCO output signal frequency that corresponds to adesired radio, intermediate, or baseband frequency to be output by themixer(s) 34 using VCO output signal OSC (e.g., when mixing an inputsignal with the local oscillator signal LO produced using VCO outputsignal OSC). The frequency for VCO output signal OSC may be identifiedusing software running on control circuitry 14 and/or using controlsignals received from external communications circuitry such as awireless access point or base station, as examples.

At operation 78, control circuitry 14 may place VCO circuitry 42 in aselected operating mode that corresponds to the identified frequency(e.g., a selected one of a first, second, third, or fourth operatingmode, in which the identified frequency is producible using VCOcircuitry 42). Control circuitry 14 may place VCO circuitry 42 in theselected operating mode using the control signals SW_(CTRL) provided toswitch network 58. Control circuitry 14 may, for example, place VCOcircuitry 42 in the selected operating mode by placing each of the fourswitching circuits 70 in switch network 58 into a respective one of thefirst and second states (e.g., as described above in connection withFIG. 3).

In addition, VCO circuitry 42 may fine-tune the frequency produced byVCO circuitry 42 (e.g., within the frequency range associated with theselected operating mode) using the control voltage V_(CTRL) provided toVCO cores 54. VCO circuitry 42 may generate corresponding VCO outputsignals OSC that are output over path 38 (FIG. 1). Mixer(s) 34 may useVCO output signals OSC (e.g., the local oscillator signals LO producedon path 38 using VCO output signals OSC) to down-convert or up-convertinput signals to a frequency corresponding to the VCO output signalfrequency identified while processing operation 76. Processing maysubsequently loop back to operation 76 via path 79 to update the VCOoutput signal frequency as needed over time.

FIGS. 6-9 are diagrams depicting different operating modes of the VCOcircuitry 42. For example, VCO circuitry 42 may be operated in each ofthe first, second, third, and fourth operating modes. In the example ofFIGS. 6-9, switch network 58 (FIG. 2) includes a first switching circuit70 (FIG. 4) coupled between VCOs 50A and 50B in parallel with capacitors56-1, a second switching circuit 70 (FIG. 4) coupled between VCOs 50Band 50C in parallel with capacitors 56-2, a third switching circuit 70(FIG. 4) coupled between VCOs 50C and 50D in parallel with capacitors56-3, and a fourth switching circuit 70 (FIG. 4) coupled between VCOs50D and 50A in parallel with capacitors 56-4. However, switch network 58and its four switching circuits 70 are not illustrated in FIGS. 6-9 soas not to unnecessarily obscure the drawings.

In each of the first, second, third, and fourth operating modes, switchnetwork 58 is adjusted to selectively control the direction of currenton each of the inductors 52 of VCO circuitry 42 (e.g., so that thecurrent flows in a clockwise or counterclockwise direction when viewedinto the plane of the page). The direction of the current betweenadjacent VCOs 50 may cause some of the capacitors 56 to effectivelyappear invisible or visible to the system in each of the operatingmodes, which allows VCO circuitry 42 to produce VCO output signals OSCat frequencies that have a linear distribution across each of the fouroperating modes, with an extended frequency range across all four of theoperating modes, and while introducing minimal phase noise. Thecapacitors 56 coupled between adjacent VCOs may effectively appearinvisible to the system when the current in the adjacent VCOs flow inopposite directions (e.g., when the current and voltage distributionsbetween the adjacent VCOs exhibit mirror symmetry about an axisextending perpendicularly between the adjacent VCOs). On the other hand,the capacitors 56 coupled between adjacent VCOs may effectively appearvisible to the system when the current in the adjacent VCOs flow in thesame direction (e.g., when the current and voltage distributions betweenthe adjacent VCOs exhibit symmetry about the axis extendingperpendicularly between the adjacent VCOs).

FIG. 6 is a diagram showing how VCO circuitry 42 may be operated in thefirst operating mode. In the first operating mode (sometimes referred toherein as “MODE0”), VCO circuitry 42 may produce VCO output signals OSCwithin a first frequency range. Switch network 58 may be configured(using switch control signals SW_(CTRL) of FIG. 2) so that the switchingcircuit 70 coupled between VCOs 50A and 50B, the switching circuit 70coupled between VCOs 50B and 50C, the switching circuit 70 coupledbetween VCOs 50C and 50D, and the switching circuit 70 coupled betweenVCOs 50D and 50A are each in the first state (i.e., where switches 72 ofFIG. 4 are closed and switches 74 of FIG. 4 are open).

Configuring switch network 58 in this way may cause the current in theinductor 52 of each VCO 50 to flow in a direction opposite to thedirection of the current in the two adjacent VCOs 50. Each VCO 50 isadjacent to one VCO 50 about horizontal axis 82 and another VCO 50 aboutvertical axis 80. As shown in FIG. 6, current I will flow through eachinductor 52 between terminals N and P of the corresponding VCO core 54in a direction illustrated from “−” to “+.” When in the first operatingmode, switch network 58 configures the voltages at terminals P and N ofVCO core 54A to vary directly with the voltages at terminals P and N ofVCO core 54B, respectively (e.g., because the switches 72 in theswitching circuit 70 coupled between VCOs 50A and 50B short theterminals P together and short the terminals N together). Equivalently,a current IA will flow from terminal N to terminal P of VCO core 54A(e.g., in a clockwise direction), whereas an opposite current IB willflow from terminal N to terminal P of VCO core 54B (e.g., in acounterclockwise direction). This current and voltage mirror symmetrybetween VCOs 50A and 50B about vertical axis 80 causes capacitors 56-1(as well as the switches in the parallel-coupled switching circuit 70)to effectively appear invisible to the system.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54B to vary directly with the voltages at terminals P andN of VCO core 54C, respectively (e.g., because the switches 72 in theswitching circuit 70 coupled between VCOs 50B and 50C short theterminals P together and short the terminals N together). Equivalently,a current IC will flow from terminal N to terminal P of VCO core 54C(e.g., in a clockwise direction), which is opposite the direction of thecurrent IB in VCO 50B. This current and voltage mirror symmetry abouthorizontal axis 82 causes capacitors 56-2 (as well as the switches inthe parallel-coupled switching circuit 70) to effectively appearinvisible to the system.

In addition, switch network 58 configures the voltages at terminals Pand N of VCO core 54C to vary directly with the voltages at terminals Pand N of VCO core 54D, respectively (e.g., because the switches 72 inthe switching circuit 70 coupled between VCOs 50C and 50D short theterminals P together and short the terminals N together). Equivalently,a current ID will flow from terminal N to terminal P of VCO core 54D(e.g., in a counterclockwise direction), which is opposite to thedirection of the current IC in VCO 50C. This current and voltage mirrorsymmetry about vertical axis 80 causes capacitors 56-3 (as well as theswitches in the parallel-coupled switching circuit 70) to effectivelyappear invisible to the system.

Finally, switch network 58 configures the voltages at terminals P and Nof VCO core 54D to vary directly with the voltages at terminals P and Nof VCO core 54A, respectively (e.g., because the switches 72 in theswitching circuit 70 coupled between VCOs 50D and 50A short theterminals P together and short the terminals N together). Current IDthus flows in a direction opposite to the direction of the current IA inVCO 50A. This current and voltage mirror symmetry about horizontal axis82 causes capacitors 56-4 (as well as the switches in theparallel-coupled switching circuit 70) to effectively appear invisibleto the system. When configured in this way (in first operating modeMODE0), VCO circuitry 42 may output VCO output signals OSC within thefirst frequency range. The control voltage V_(CTRL) provided to VCOcores 54 may further tune the frequency of VCO output signals OSC withinthe first frequency range.

FIG. 7 is a diagram showing how VCO circuitry 42 may be operated in thesecond operating mode. In the second operating mode (sometimes referredto herein as “MODE1”), VCO circuitry 42 may produce VCO output signalsOSC within a second frequency range (e.g., at lower frequencies than thefirst frequency range). Switch network 58 may be configured so that theswitching circuit 70 coupled between VCOs 50A and 50B and the switchingcircuit 70 coupled between VCOs 50C and 50D are each in the second state(i.e., where switches 72 of FIG. 4 are open and switches 74 of FIG. 4are closed). At the same time, switch network 58 may be configured sothat the switching circuit 70 coupled between VCOs 50B and 50C and theswitching circuit 70 coupled between VCOs 50D and 50A are each in thefirst state (i.e., where switches 72 of FIG. 4 are closed and switches74 of FIG. 4 are open).

Configuring switch network 58 in this way may cause the current in theinductor 52 of each VCO 50 to flow in the same direction as the adjacentVCO 50 about vertical axis 80 but in the opposite direction as theadjacent VCO 50 about horizontal axis 82. For example, as shown in FIG.7, switch network 58 configures the voltages at terminals P and N of VCOcore 54A to vary oppositely (inversely) with the voltages at terminals Pand N of VCO core 54B, respectively (e.g., because the switches 74 inthe switching circuit 70 coupled between VCOs 50A and 50B short theterminal P in VCO 50A to the terminal N in VCO 50B and short theterminal N in VCO 50A to the terminal P in VCO 50B). Equivalently,current IA will flow from terminal N to terminal P of VCO core 54A(e.g., in a clockwise direction) while current IB flows in the samedirection, from terminal P to terminal N of VCO core 54B (e.g., in theclockwise direction). This current and voltage symmetry between VCOs 50Aand 50B about vertical axis 80 causes capacitors 56-1 to effectivelyappear visible to the system.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54C to vary oppositely (inversely) with the voltages atterminals P and N of VCO core 54BD, respectively (e.g., because theswitches 74 in the switching circuit 70 coupled between VCOs 50C and 50Dshort the terminal P in VCO 50C to the terminal N in VCO 50D and shortthe terminal N in VCO 50C to the terminal P in VCO 50D). Equivalently,current IC will flow from terminal P to terminal N of VCO core 54C(e.g., in a counterclockwise direction) while current ID flows in thesame direction, from terminal N to terminal P of VCO core 54B (e.g., inthe counterclockwise direction). This current and voltage symmetrybetween VCOs 50C and 50D about vertical axis 80 causes capacitors 56-3to effectively appear visible to the system.

At the same time, switch network 58 configures the voltages at terminalsP and N of VCO core 54B to vary directly with the voltages at terminalsP and N of VCO core 54C, respectively (e.g., because the switches 72 inthe switching circuit 70 coupled between VCOs 50B and 50C short theterminals P together and short the terminals N together). Current ICthus flows in a direction opposite to the direction of the current IB inVCO 50B. This current and voltage mirror symmetry about horizontal axis82 causes capacitors 56-2 (as well as the switches in theparallel-coupled switching circuit 70) to appear invisible to thesystem.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54D to vary directly with the voltages at terminals P andN of VCO core 54A, respectively (e.g., because the switches 72 in theswitching circuit 70 coupled between VCOs 50D and 50A short theterminals P together and short the terminals N together). Current IDthus flows in a direction opposite the direction of current IA in VCO50A. This current and voltage mirror symmetry about horizontal axis 82causes capacitors 56-4 (as well as the switches in the parallel-coupledswitching circuit 70) to appear invisible to the system. When configuredin this way (in second operating mode MODE1), VCO circuitry 42 mayoutput VCO output signals OSC within the second frequency range. Thecontrol voltage V_(CTRL) provided to VCO cores 54 may further tune thefrequency of VCO output signals OSC within the second frequency range.

FIG. 8 is a diagram showing how VCO circuitry 42 may be operated in thethird operating mode. In the third operating mode (sometimes referred toherein as “MODE2”), VCO circuitry 42 may produce VCO output signals OSCwithin a third frequency range (e.g., at lower frequencies than thesecond frequency range). Switch network 58 may be configured so that theswitching circuit 70 coupled between VCOs 50A and 50B and the switchingcircuit 70 coupled between VCOs 50C and 50D are each in the first state(i.e., where switches 74 of FIG. 4 are open and switches 72 of FIG. 4are closed). At the same time, switch network 58 may be configured sothat the switching circuit 70 coupled between VCOs 50B and 50C and theswitching circuit 70 coupled between VCOs 50D and 50A are each in thesecond state (i.e., where switches 72 of FIG. 4 are open and switches 74of FIG. 4 are closed).

Configuring switch network 58 in this way may cause the current in theinductor 52 of each VCO 50 to flow in the same direction as the adjacentVCO 50 about horizontal axis 82 but in the opposite direction as theadjacent VCO 50 about vertical axis 80. For example, as shown in FIG. 8,switch network 58 configures the voltages at terminals P and N of VCOcore 54B to vary oppositely (inversely) with the voltages at terminals Pand N of VCO core 54C, respectively (e.g., because the switches 74 inthe switching circuit 70 coupled between VCOs 50B and 50C short theterminal P in VCO 50B to the terminal N in VCO 50C and short theterminal N in VCO 50B to the terminal P in VCO 50C). Equivalently,current IB will flow from terminal N to terminal P of VCO core 54B(e.g., in a counterclockwise direction) while current IC flows in thesame direction, from terminal P to terminal N of VCO core 54C (e.g., inthe counterclockwise direction). This current and voltage symmetrybetween VCOs 50B and 50C about horizontal axis 82 causes capacitors 56-2to effectively appear visible to the system.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54D to vary oppositely (inversely) with the voltages atterminals P and N of VCO core 54BA, respectively (e.g., because theswitches 74 in the switching circuit 70 coupled between VCOs 50D and 50Ashort the terminal P in VCO 50D to the terminal N in VCO 50A and shortthe terminal N in VCO 50D to the terminal P in VCO 50A). Equivalently,current ID will flow from terminal P to terminal N of VCO core 54D(e.g., in a clockwise direction) while current IA flows in the samedirection, from terminal N to terminal P of VCO core 54A (e.g., in theclockwise direction). This current and voltage symmetry between VCOs 50Dand 50A about horizontal axis 82 causes capacitors 56-4 to effectivelyappear visible to the system.

At the same time, switch network 58 configures the voltages at terminalsP and N of VCO core 54A to vary directly with the voltages at terminalsP and N of VCO core 54B, respectively (e.g., because the switches 72 inthe switching circuit 70 coupled between VCOs 50A and 50B short theterminals P together and short the terminals N together). Current IBthus flows in a direction opposite to the direction of the current IA inVCO 50A. This current and voltage mirror symmetry about vertical axis 80causes capacitors 56-1 (as well as the switches in the parallel-coupledswitching circuit 70) to appear invisible to the system.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54C to vary directly with the voltages at terminals P andN of VCO core 54D, respectively (e.g., because the switches 72 in theswitching circuit 70 coupled between VCOs 50C and 50D short theterminals P together and short the terminals N together). Current IDthus flows in a direction opposite the direction of current IC in VCO50C. This current and voltage mirror symmetry about vertical axis 80causes capacitors 56-3 (as well as the switches in the parallel-coupledswitching circuit 70) to appear invisible to the system. When configuredin this way (in third operating mode MODE2), VCO circuitry 42 may outputVCO output signals OSC within the third frequency range. The controlvoltage V_(CTRL) provided to VCO cores 54 may further tune the frequencyof VCO output signals OSC within the third frequency range.

FIG. 9 is a diagram showing how VCO circuitry 42 may be operated in thefourth operating mode. In the third fourth mode (sometimes referred toherein as “MODE3”), VCO circuitry 42 may produce VCO output signals OSCwithin a fourth frequency range (e.g., at lower frequencies than thethird frequency range). Switch network 58 may be configured so that theswitching circuit 70 coupled between VCOs 50A and 50B, the switchingcircuit 70 coupled between VCOs 50C and 50D, the switching circuit 70coupled between VCOs 50B and 50C, and the switching circuit 70 coupledbetween VCOs 50D and 50A are each in the second state (i.e., whereswitches 72 of FIG. 4 are open and switches 74 of FIG. 4 are closed).

Configuring switch network 58 in this way may cause the current in theinductor 52 of each VCO 50 to flow in the same direction as all of theother VCOs 50 in VCO circuitry 42. For example, as shown in FIG. 9,switch network 58 configures the voltages at terminals P and N of VCOcore 54A to vary oppositely (inversely) with the voltages at terminals Pand N of VCO core 54B, respectively (e.g., because the switches 74 inthe switching circuit 70 coupled between VCOs 50A and 50B short theterminal P in VCO 50A to the terminal N in VCO 50B and short theterminal N in VCO 50A to the terminal P in VCO 50B). Equivalently,current IA will flow from terminal N to terminal P of VCO core 54A(e.g., in a clockwise direction) while current IB flows in the samedirection, from terminal P to terminal N of VCO core 54B (e.g., in theclockwise direction). This current and voltage symmetry between VCOs 50Aand 50B about vertical axis 80 causes capacitors 56-1 to effectivelyappear visible to the system.

Similarly, switch network 58 configures the voltages at terminals P andN of VCO core 54B to vary oppositely (inversely) with the voltages atterminals P and N of VCO core 54C, respectively (e.g., because theswitches 74 in the switching circuit 70 coupled between VCOs 50B and 50Cshort the terminal P in VCO 50B to the terminal N in VCO 50C and shortthe terminal N in VCO 50B to the terminal P in VCO 50C). Equivalently,current IB will flow from terminal P to terminal N of VCO core 54B(e.g., in the clockwise direction) while current IC flows in the samedirection, from terminal N to terminal P of VCO core 54C (e.g., in theclockwise direction). This current and voltage symmetry between VCOs 50Band 50C about horizontal axis 82 causes capacitors 56-2 to effectivelyappear visible to the system.

In addition, switch network 58 configures the voltages at terminals Pand N of VCO core 54C to vary oppositely (inversely) with the voltagesat terminals P and N of VCO core 54D, respectively (e.g., because theswitches 74 in the switching circuit 70 coupled between VCOs 50C and 50Dshort the terminal P in VCO 50C to the terminal N in VCO 50D and shortthe terminal N in VCO 50C to the terminal P in VCO 50D). Equivalently,current IC will flow from terminal N to terminal P of VCO core 54C(e.g., in the clockwise direction) while current ID flows in the samedirection, from terminal P to terminal N of VCO core 54D (e.g., in theclockwise direction). This current and voltage symmetry between VCOs 50Cand 50D about vertical axis 80 causes capacitors 56-3 to effectivelyappear visible to the system.

Finally, switch network 58 also configures the voltages at terminals Pand N of VCO core 54D to vary oppositely (inversely) with the voltagesat terminals P and N of VCO core 54A, respectively (e.g., because theswitches 74 in the switching circuit 70 coupled between VCOs 50D and 50Ashort the terminal P in VCO 50D to the terminal N in VCO 50A and shortthe terminal N in VCO 50D to the terminal P in VCO 50A). Current ID thusflows from terminal P to terminal N of VCO core 54D (e.g., in theclockwise direction) while current IA flows in the same direction, fromterminal N to terminal P of VCO core 54A (e.g., in the clockwisedirection). This current and voltage symmetry between VCOs 50D and 50Aabout horizontal axis 82 causes capacitors 56-4 to effectively appearvisible to the system. When configured in this way (in fourth operatingmode MODE3), VCO circuitry 42 may output VCO output signals OSC withinthe fourth frequency range. The control voltage V_(CTRL) provided to VCOcores 54 may further tune the frequency of VCO output signals OSC withinthe third frequency range.

FIG. 10 is a plot showing how operating VCO circuitry 42 in the first,second, third, and fourth operating modes of FIGS. 6-9 may serve toextend the frequency range of VCO circuitry 42. Plot 100 of FIG. 10plots the frequency of the VCO output signals as a function of theactive VCO in scenarios where switched capacitors are coupled betweeneach of four VCOs and only one VCO is active at any given time forproducing the VCO output signals. As shown by lines 106 of plot 100,each VCO may produce a corresponding frequency range, subject to arelatively large overlap 104 between each VCO. The presence of overlap104 between each VCO may limit the overall frequency range across allfour VCOs to overall frequency range R1.

Plot 102 of FIG. 10 plots the frequency of VCO output signals OSC as afunction of the operating mode of VCO circuitry 42. As shown by lines110 of plot 102, first operating mode MODE0 may produce a firstfrequency range, second operating mode MODE1 may produce a secondfrequency range that covers lower frequencies than the first frequencyrange, third operating mode MODE2 may produce a third frequency rangethat covers lower frequencies than the second frequency range, andfourth operating mode MODE3 may produce a fourth frequency range thatcovers lower frequencies than the third frequency range. Controlcircuitry 14 may tune the frequency of VCO output signals OSC withineach frequency range using control voltage V_(CTRL) (FIG. 2).

As shown by curves 110, the frequency response of VCO circuitry 42 islinear across all four operating modes, with an overlap 108 between eachoperating mode that is significantly smaller than the overlap 104associated with plot 100. This may allow VCO circuitry 42 to exhibit awider overall frequency range R2 across all four operating modes thanthe frequency range R1 associated with plot 100.

The examples of FIGS. 2-10 are merely illustrative. If desired, VCOcircuitry 42 may have fewer than four operating modes (e.g., two orthree operating modes), may have more than four operating modes (e.g.,six or more operating modes), may include only two VCOs 50 that arecoupled together by a single switching circuit 70 and a single pair ofcapacitors 56, or may include more than four VCOs 50. Inductors 52,which may sometimes be referred to herein as coils, may have anoctagonal shape (e.g., as shown in FIGS. 2 and 6-9) or may have othershapes (e.g., a circular shape, an elliptical shape, or any other shapehaving any desired number of curved and/or straight segments).

The methods and operations described above in connection with FIGS. 1-10may be performed by the components of device 10 using software,firmware, and/or hardware (e.g., dedicated circuitry or hardware).Software code for performing these operations may be stored onnon-transitory computer readable storage media (e.g., tangible computerreadable storage media) stored on one or more of the components ofdevice 10 (e.g., storage circuitry 16 of FIG. 1). The software code maysometimes be referred to as software, data, instructions, programinstructions, or code. The non-transitory computer readable storagemedia may include drives, non-volatile memory such as non-volatilerandom-access memory (NVRAM), removable flash drives or other removablemedia, other types of random-access memory, etc. Software stored on thenon-transitory computer readable storage media may be executed byprocessing circuitry on one or more of the components of device 10(e.g., processing circuitry 18 of FIG. 1, etc.). The processingcircuitry may include microprocessors, central processing units (CPUs),application-specific integrated circuits with processing circuitry, orother processing circuitry.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. Local oscillator circuitry comprising: a firstvoltage-controlled oscillator (VCO); a second VCO; at least onecapacitor coupled between the first VCO and the second VCO; and at leastone switch coupled between the first VCO and the second VCO andconfigured to adjust current direction in the first VCO and in thesecond VCO.
 2. The local oscillator circuitry of claim 1, wherein atleast the first VCO and the second VCO are configured to generate alocal oscillator signal.
 3. The local oscillator circuitry of claim 2,wherein the local oscillator signal has a first frequency in a firstfrequency range when current flows in a first direction in the first VCOand has a second frequency in a second frequency range that is at leastpartially non-overlapping with respect to the first frequency range whencurrent flows in a second direction in the first VCO opposite the firstdirection.
 4. The local oscillator circuitry of claim 1, wherein the atleast one switch is coupled between the first VCO and the second VCO inparallel with the at least one capacitor.
 5. The local oscillatorcircuitry of claim 4, wherein the at least one capacitor comprises afirst capacitor and a second capacitor coupled between the first VCO andthe second VCO in parallel with the at least one switch.
 6. The localoscillator of claim 1, wherein the first VCO comprises a first VCO coreand a first inductor and the second VCO comprises a second VCO core anda second inductor.
 7. The local oscillator of claim 6, wherein the atleast one switch and the at least one capacitor are coupled between thefirst VCO core and the second VCO core.
 8. The local oscillator of claim1, wherein the first VCO has a first terminal and a second terminal, thesecond VCO has a third terminal and a fourth terminal, and the at leastone switch comprises: a first switch coupled between the first terminaland the third terminal; and a second switch coupled between the secondterminal and the fourth terminal.
 9. The local oscillator of claim 8,wherein the at least one switch further comprises: a third switchcoupled between the first terminal and the fourth terminal; and a fourthswitch coupled between the second terminal and the third terminal. 10.An electronic device comprising: wireless circuitry configured to conveyradio-frequency signals using a local oscillator signal; a firstvoltage-controlled oscillator (VCO); a second VCO, wherein at least thefirst VCO and the second VCO are configured to generate the localoscillator signal; a capacitor coupled between the first VCO and thesecond VCO; and at least one switch coupled between the first VCO andthe second VCO and configured to reverse current direction in the firstVCO and in the second VCO.
 11. The electronic device of claim 10,wherein the first VCO has a first terminal and a second terminal, thesecond VCO has a third terminal and a fourth terminal, and the capacitoris coupled between the first terminal and the third terminal.
 12. Theelectronic device of claim 11, further comprising: an additionalcapacitor coupled between the second terminal and the fourth terminal.13. The electronic device of claim 12, wherein the at least one switchcomprises: a first switch coupled between the first terminal and thefourth terminal; and a second switch coupled between the second terminaland the third terminal.
 14. The electronic device of claim 13, whereinthe at least one switch further comprises: a third switch coupledbetween the first terminal and the third terminal; and a fourth switchcoupled between the second terminal and the fourth terminal.
 15. Theelectronic device of claim 10, wherein the local oscillator signal is ata first frequency in a first frequency range when current flows in afirst direction in the first VCO and is at a second frequency in asecond frequency range when current flows in a second direction in thefirst VCO opposite the first direction, the second frequency range beingat least partially non-overlapping with respect to the first frequencyrange, wherein the first VCO comprises a first VCO core and a firstinductor, the second VCO comprises a second VCO core and a secondinductor, and the electronic device further comprises: one or moreprocessors configured to provide a control signal to the first VCO corethat adjusts the first frequency within the first frequency range whenthe current flows in the first direction and that adjusts the secondfrequency within the second frequency range when the current flows inthe second direction.
 16. A method of operating voltage-controlledoscillator (VCO) circuitry having a first VCO, a second VCO, at leastone capacitor coupled between the first VCO and the second VCO, and atleast one switch coupled between the first VCO and the second VCO, themethod comprising: with the at least one switch, placing the first VCOand the second VCO in a first state in which current flows in a firstdirection in the first VCO; with the first VCO and the second VCO,outputting a first VCO signal having a first frequency within a firstrange of frequencies while the first VCO and the second VCO are in thefirst state; with the at least one switch, placing the first VCO and thesecond VCO in a second state in which current flows in a seconddirection in the first VCO, the second direction being opposite thefirst direction; and with the first VCO and the second VCO, outputting asecond VCO signal having a second frequency within a second range offrequencies that is at least partially non-overlapping with respect tothe first range of frequencies while the first VCO and the second VCOare in the second state.
 17. The method of claim 16, wherein currentflows in the first direction in the second VCO in the first state and inthe first direction in the second VCO in the second state.
 18. Themethod of claim 16, wherein current flows in the first direction in thesecond VCO in the first state and in the second direction in the secondVCO in the second state.
 19. The method of claim 16, wherein currentflows in the second direction in the second VCO in the first state andin the second direction in the second VCO in the second state.
 20. Themethod of claim 16, wherein current flows in the second direction in thesecond VCO in the first state and in the first direction in the secondVCO in the second state.